1. Field of the Invention
The present invention relates to a flat lamp for emitting light to a surface area and a liquid crystal display using the same, and more particularly to a flat lamp implemented as an independent illuminator.
2. Background of the Related Art
A liquid crystal display (LCD) device generally provides image effects using characteristics attained by injecting liquid crystals between a lower substrate having thin film transistors and an upper substrates having color filters. In accordance with the operating principles of the LCD device, once a voltage is applied to transparent electrode plates disposed inside glass substrates, the direction of molecular motion of liquid crystals is separated. Accordingly, the amount of light passing through gaps between the liquid crystals varies, thereby creating an image.
Such a LCD device has an overall smaller size, reduced weight, and lower power consumption as compared to conventional cathode ray tube devices. However, since a LCD panel of a LCD device is non-luminous, the LCD panel needs an additional light source, i.e. a backlight assembly. Light sources used for the backlight assembly may be classified into at least three different categories: a point light source of a white halogen lamp; a linear light source of a fluorescent lamp; and a planar light source of an electro-luminescence (EL) or light emitting diode (LED). However, the light source which is widely used in conventional backlight assemblies is a linear light source using a cold cathode fluorescence lamp (CCFL) that has a long lifespan and excellent spectroscopic characteristics.
Reference will now be made in detail to a backlight assembly to which the CCFL is applied in a LCD device, examples of which are illustrated in the accompanying drawings.
FIG. 1 shows an edge-type backlight assembly to which a fluorescent lamp is applied in a liquid crystal display according to a related art, and FIG. 2 shows a disassembled plan view of a backlight assembly according to the related art shown in FIG. 1.
In FIG. 1, a backlight assembly is placed at a rear surface of a LCD panel (not shown in the drawing) which displays image data, and a main support 1 and a cover 3 that protects the main support 1. A lamp assembly 10 is placed at one end of the main support 1, and a light guiding plate (LGP) 5 that transmits light emitted from the lamp assembly to the LCD panel is placed at a lateral side of the lamp assembly. A reflection sheet 4 for reflecting any light that may leak out from the lamp assembly is placed at a lower surface of the light guiding plate 5. A lower diffusion sheet 6 and an upper diffusion sheet 9 that diffuse incident light coming from the light guiding plate 5 are placed at an upper surface of the light guiding plate 5. A lower prism sheet 7 and an upper prism sheet 8 that condense and transmit light to the LCD panel are placed between the lower diffusion sheet 6 and the upper diffusion sheet 9. Accordingly, the backlight assembly requires at least the light guiding plate 5, the lower diffusion sheet 6, the upper diffusion sheet 9, the lower prism sheet 7, and the upper prism sheet 8 to uniformly supply light irradiated from the fluorescent lamp to the display surface.
In FIG. 2, the process of assembling the backlight assembly is performed by inserting a high pressure side lamp wire 13a and a low pressure side lamp wire 13b of a connector 16 into a high pressure lamp holder 12a and a low pressure lamp holder 12b, respectively, and then soldering the high pressure side lamp wire 13a and the low pressure side lamp wire 13b to a high pressure side and a low pressure side of the lamp 11, respectively. Then, the lamp assembly is completed by mounting a soldering part 14 of the lamp on a lamp housing 15 by covering a soldering part of the lamp with the lamp holders of the lamp. Subsequently, the lamp assembly is placed into the main support 1, and the cover 3 is inserted into a light entrance of the main support 1 in order to protect the lamp assembly from any external shocks. Then after the reflection sheet 4 has been mounted on an internal bottom surface of the main support 1, the light guiding plate 5 is inserted inside an internal gap of the lamp housing. It is important that the gap dimensions and planarity of the lamp housing remain straight. Finally, the lower diffusion sheet 6, the lower prism sheet 7, the upper prism sheet 8, and the upper diffusion sheet 9 are sequentially assembled into an upper part of the light guiding plate 5.
The above backlight assembly emitting light by generating a glow discharge in the lamp once a power source is applied by connecting the connector 16 to a power supply. The light generated by the lamp is incident on the light entrance surface of the light guiding plate 5, and is reflected and scattered by printed dots disposed on a lower surface of the light guiding plate 5. Additionally, the reflection sheet 4 prevents light loss by reflecting any light that failed to be reflected and scattered by the printed dots of the guiding plate 5 back through a rear surface of the guiding plate 5. Then, the light is condensed in a vertical direction through the lower prism sheet 7 and upper prism sheet 8 and is scattered by the diffusion sheet 9. Finally, the light passes through the diffusion sheet 9 and is supplied to the rear surface of the LCD panel to represent image data.
As mentioned above, since the backlight assembly requires at least the light guiding plate 5, a process for forming a pattern of the printed dots on the lower surface of the guiding plate is required. In addition, a high technology process for casting and injection molding is also required. Therefore, the backlight assembly of the related art is high in product cost and low in product yield due to the complicated part sourcing and fabrication processes involved. Generally, defects of the backlight assembly of the related art are created in the sheet structures such as the light guiding plate, prism sheets, and reflection sheet. Specifically, one defect involves the bending of the light guiding plate which is short for its overall dimensions, and another defect involves scratches and/or particles that are found on the light guiding plate, prism sheets and reflection sheet. Therefore, there is a limit on enlarging the size of a backlight assembly and accordingly, on increasing of the size of the display.
In order to solve the above problems, a direct-type backlight assembly is proposed that enables light to be supplied to the diffusion sheet directly without use of a light guiding plate by arranging a plurality of lamps on a rear surface of the diffusion sheet. However, the direct-type backlight assembly still requires diffusion and prism sheets to provide uniform light. Moreover, the edge- or direct-type backlight assemblies also fail to provide uniform light to an entire display surface with high brightness as well as wide visible angles.